The present invention relates to improvements in mechanisms for the preparation of mineral mixtures, particularly of a rough washed coal in a jig controlled by compressed air wherein the liquid mixture of the coal is given a pulsed motion by means of pulsations of compressed air. The invention particularly relates to an improved valve structure for controlling the air pulsations in connecting an opening beneath the surface of the container for the coal connected alternately to compressed air and to atmosphere.
In wet jigging machines for preparing coal or other minerals, a large container is provided through which a slurry of coal is flowed, and pulse openings open downwardly beneath the surface of the liquid in the container and the openings are supplied with air pulsations at a controlled frequency. In the control of these pulsations both for the supply of compressed air and the release of air to the atmosphere, various forms of valves have been employed. Valves frequently used employ slide mechanisms or disks or mushroom-type poppet valves. Examples of control mechanisms are shown and described in U.S. Pat. Nos. 4,019,981 and 4,485,010.
The present invention relates to a combination embodying an improved mechanism wherein the compressed air from an air dome and the venting of the air into the outside atmosphere for the jig is controlled and where the timing can be controlled to conveniently regulate the duration of opening as well as the time of occurrence of opening.
In a jigging machine the space available for the control is limited and thus the conduit cross-section for the pressurized air conduits and the conduits and the conduits vented to atmosphere is crucial. Also, the path of flow of the compressed air and the venting of air to atmosphere must be such that the timing of the airflow can be accurately controlled. That is, the control valve arrangement for the pulses must be such that there is an absence of throttling losses in pressure and timing in the passages and particularly in the valve structure.
An object of the present invention is to provide a pulse generator valve which is constructed to require a limited space and which has minimum flow losses both in the valve itself and the manner in which it can be connected to the airflow conduits or passages.
A further object of the invention is to provide an improved pulse control valve wherein the valve timing is very easily changed and regulated and wherein the duration of time of the valve opening can be readily controlled and wherein the opening time can be readily regulated and controlled.
In accordance with the objects, a feature of the invention is to provide a pulse control valve which employs butterfly valve plates mounted on a common shaft with compartments therein connecting to ports which extend parallel through the chambers for the conduction of pressurized air and the conduction of air from the jig to the atmosphere in a straight-through linear path. A reduction of flow losses in the valve is achieved in various ways. One way is that the construction and principles of the valve permit a relatively large conduit cross-section with no deflections of the airstream being required During a jigging machine cycle, both the conduit from the air dome to the air chamber beneath the liquid as well as that from the air chamber to the outside atmosphere, must be closed during at least half the cycle time. In the present valve employing a butterfly valve plate, the valve rotates in a correspondingly large cylindrical housing whereby the opening and closing times are defined as approximated by the area of the ports and opening in the cylindrical housing wall. As distinguished from previous rotary slide valve controls, a jigging cycle is already terminated after a revolution of 180.degree.. A full cycle is repeated twice for each full rotation so that utilization of half the rotational speed does not detract from the steepness of the reaction of airflow to the valve operation. The butterfly valve plate thus releases twice during each revolution. The arrangement permits the provision of a cross-sectional area of the ports and conduits leading thereto to be larger than possible with devices heretofore available. This permits the maximum pressure in the air chamber, beneath the surface of the liquid to be reached sooner. This also permits the release to be reached sooner. Therefore, the pressure curve of the pressure within the chamber beneath the liquid surface which is approximately a trapezoidal curve, more greatly approximates a desired rectangular curve. The butterfly valve plate has a minimal flow inhibiting effect and requires a minimu of structural cross-sectional space which, of course, is less than that of a flat slide valve.
A further object of the invention is to provide a pulse control valve of fewer parts and of simpler construction than valves heretofore available such as that provided by a rotary piston type of valve.
In accordance with a preferred embodiment, the pressurized air admission conduits and the conduits for releasing air to atmosphere are not shifted relative to each other in an axial direction. As a result, the flow need not be deflected and the resistance to flow and thus the delay in pressurization and release is minimized.
In accordance with a preferred embodiment, the angle between the butterfly valve plate in the pressurized air conduit and the butterfly valve plate of the conduits for outside atmosphere is variable. The points in time for opening and closing can thus be varied and controlled.
As a further feature of a preferred embodiment of the invention, the cross-sectional area of the ports in the valve which communicate with the pressurized and release passages are variable by means of a lining or bushing within the valve. The characteristic can be independently varied both for the inflowing pressurized air as well as for the outflowing atmospheric air and the total opening can be varied as well as the time of beginning or ending of the flow. The characteristic of flow in each direction, that is, of pressurized air and of air release can be varied independently of one another.
In accordance with another feature of the invention, a butterfly valve plate operates within a cylindrical housing and a gap is provided between the edge of the valve plate and the housing wall. This permits a leakage flow on the order of magnitude of tenths of a millimeter of liters, but this does not recognizably detract from the operation of the pulsing valve. The gap, however, eliminates the need for lubrication, and eliminates wear and the need for frequent servicing or replacement.
Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings, in which: